Microsoft 365 Error Codes

Fix Microsoft Loop Using onmicrosoft Address Instead of Custom Domain

Maira Mehtab Sep 22, 2026 870 views

Question details

Users need to resolve an error where Microsoft Loop auto-suggests the onmicrosoft.com address rather than the newly configured custom domain.

Product: Microsoft Loop / Microsoft 365
Device & OS: not provided
Scenario: Assigning tasks or mentioning contacts in Microsoft Loop after transitioning to a custom domain.
Observed behavior: Loop continues to resolve the user's onmicrosoft.com address. While manually typing the custom address works, selecting the auto-suggested contact triggers an IT policy error.

Before you start

Verify that your custom domain is correctly configured as the default domain in the Microsoft 365 admin center and clear your browser cache before requesting further backend support.

Solution 1Recommended

Submit a Support Request via Microsoft 365 Admin Center

Use this solution to have Microsoft engineers inspect and fix backend directory identity and synchronization issues that local troubleshooting cannot resolve.

Because actions like signing out, clearing browser cache, and removing credentials from the Windows Credential Manager often do not resolve this, the problem is likely tied to background identity services.

Microsoft 365 support has the necessary permissions to inspect backend directory configurations and synchronization logs to fix the domain resolution error.

Log in to Admin Center

Navigate to the Microsoft 365 admin center (admin.microsoft.com) and log in using your administrator credentials.

Open Help & Support

Click on the 'Support' icon or the 'Help & support' option located in the bottom right corner or the left-hand navigation menu.

Create a New Service Request

Type a brief description of the Loop domain issue, press Enter, and then click 'Contact Support' to open a new ticket.

Provide Error Details

Fill out the ticket with the custom domain, the onmicrosoft address, the exact IT policy error text, and list the local troubleshooting steps you have already completed.

Administrator Privileges Required: If you are a standard user, you do not have access to the admin center. You must contact your organization's IT department or Microsoft 365 administrator to perform these steps.

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Frequently Asked Questions

Why does Microsoft Loop default to the onmicrosoft.com address?

This usually occurs due to a delay or failure in backend identity synchronization after a custom domain is added to Microsoft 365, causing Loop to fetch outdated directory data.

Will clearing my browser cache fix the Loop domain issue?

While clearing the cache or removing credentials from Windows Credential Manager is recommended as a first step, it often does not resolve the issue if the root cause is a backend directory mismatch on Microsoft's servers.

How do I find my Microsoft 365 admin to submit this ticket?

Your admin is typically the person who set up your Microsoft 365 account. This is usually someone in your IT department, an external IT managed service provider, or the business owner.

Microsoft Office Error Codes